Hydraulic assemblies of said type are used widely and in diverse embodiments. In particular master brake cylinders of various kinds have a cavity which is normally formed as a blind bore in which one or multiple cylinder pistons are displaced axially, which pistons delimit in the cavity one or multiple pressure chambers which are filled with pressure liquid and in which brake pressure is generated because of the piston displacement.
In order to ensure correct functioning of the assembly, the cavity must have at least one bore portion with a target diameter of defined tolerance into which the cylinder piston is displaced in a sealed-off manner. Furthermore, for an intended durability, it is necessary for the inner wall of the cavity to have a defined minimum hardness and surface quality at least in portions on which a sealing element slides and/or which come into contact with the piston at least temporarily, in order to reduce wear and friction forces.
In most hydraulic assemblies of said type, the cavity is introduced into a main body composed of an aluminum alloy which has relatively low hardness.
In order to ensure the abovementioned requirements for the bore portion(s) in question in the cavity, it is known to form the cavity as a blind bore and, by way of a cutting manufacturing process—for example by way of drilling or milling—to firstly provide said cavity with a pre-drilling diameter which is smaller than the target diameter. Subsequently, the pre-drilling diameter is increased to the target diameter, likewise in a cutting manner, by way of reaming or honing, and in the process the tips, waves and ridges in the surface which arose from the previous machining are abraded and the roughness depth and roughness of the inner wall thus reduced. Afterwards, the cavity or the entire main body are provided by means of electrochemistry with a separate protective layer—for example are anodized or electrochemically oxidized. The main body has to be repeatedly washed or cleaned after the individual process steps in order to remove the chips, cooling lubricants or electrolytes.